They have to do with the remote control protocols. Signal gap is the delay between each signal that the remote sends. Signal length is how many 0s and 1s are sent for each code. Repeat codes are used by some remotes to indicate that you're holding a button down -- instead of just sending the same key over and over, it sends the key once and then sends a special code that indicates it's being held. Typical remote controls use a 38KHz carrier wave for modulation, and that normally has a 50% duty cycle.
RC-MM was defined by Philips to be a multi-media IR protocol to be used in wireless keyboards, mice and game pads. For these purposes the commands had to be short and have low power requirements. Whether the protocol is actually used for these purposes today is unknown to me. What I do know is that some Nokia digital satellite receivers use the protocol (9800 series). Features 12 bits or 24 bits per message Pulse position coding, sending 2 bits per IR pulse Carrier frequency of 36kHz Message time ranges from 3.5 to 6.5 ms, depending on data content Repetition time 28 ms (36 messages per second) Manufacturer Philips Transmission timing: In this diagram you see the most important transmission times. The message time is the total time of a message, counting form the beginning of the first pulse until the end of the last pulse of the message. This time can be 3.5 to 6.5 ms, depending on the data content and protocol used. The signal free time is the time in which no signal ma...
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